1. Field of the Invention
The present invention relates to a process for preparing polyisocyanurate foam having properties of low smoke generation, low friability and does not burst (not scattered by contact with a flame) and which has excellent heat and flame-resistance.
2. Description of the Prior Arts
Polyisocyanurate foams can be prepared by mixing and stirring an organic polyisocyanate, an isocyanate-trimerization catalyst, a blowing agent, and if necessary a surfactant(Japanese Patent Publications Nos. 33910/1970 and 2269/1971).
The polyisocyanurate foams have excellent heat-resistance and flame-resistance caused by the isocyanurate linkage, but have the disadvantages of friability and bursting by contact with a flame and smoke-generation at the initial stage of contact with a flame.
In order to improve the disadvantages, processes for preparing various modified polyisocyanurate foams have been proposed, for example the use of a polyether as a modifier (Japanese Patent Publication Nos. 42386/1971 and 2269/1971); the use of a polyester as a modifier (Japanese Patent Publication No. 28919/1972) introduction of a polyoxazolidone linkage (Japanese Patent Publication No. 32800/1974); use of a polyol having a molecular weight of higher than 200 and a polyether diol having a molecular weight of lower than 200 as a modifier (Japanese Unexamined Patent Publication No. 101497/1973); use of a precondensate of xylene resin (Japanese Patent Publication No. 32757/1972); introduction of a polycarbodiimido linkage (Japanese Patent Publication No. 4591/1971); introduction of a urethane linkage and carbodiimide linkage (Japanese Patent Unexamined Publication No. 30796/1972). The modified polyisocyanurate foams have improved friability and bursting properties which are imparted by the modification, but still have the disadvantages of poor flame-resistance and flame-retardance and high smoke-generation. No process for preparing a polyisocyanurate foam having simultaneously five desirable characteristics of low-smoke-generation, low friability, high flame-resistance, high flame-retardance and high heat-resistance (dimensional stability under high temperature) has been proposed.
The inventors have studied a process for preparing a polyisocyanurate foam having said five characteristics.